1. Field of the Invention
The present invention relates to an optical fiber ribbon and an optical fiber cable using the same.
2. Description of the Related Art
As an optical fiber ribbon which is formed by integrating a plurality of optical fibers in a ribbon shape, followings can be named for example.
In Japanese Unexamined Patent Publication Sho. 61(1986)-73112, a ribbon-type optical unit 1105 is disclosed, wherein, as shown in FIG. 39, the ribbon-type optical unit 1105 is configured such that a plurality of coated optical fibers 1103 each of which includes a coating layer 1102 made of an ultraviolet ray curable resin around an optical fiber 1101 are arranged in parallel to form an optical fiber assembled body, and a protective layer 1104 made of an ultraviolet ray curable resin is integrally formed on the optical fiber assembled body in a state that the protective layer 1104 is not adhered to the coating layers 1102. This ribbon type optical unit 1105 is characterized in that assuming an outer diameter of the coated optical fiber 1103 as X, the number of the coated optical fibers 1103 which form the optical fiber assembled body as n, a thickness and a width of the ribbon-type optical unit 105 as H and L, relationships 1.1≦H/X≦1.45, 1.0<L/nX≦1.08 are established.
In Japanese Unexamined Utility Model Publication Hei.4(1992)-75304, as shown in FIG. 40A and FIG. 40B, in an optical fiber ribbon, a color layer is formed on an outermost periphery of each coated optical fiber and an overall coating layer is formed over the whole periphery of the coated optical fibers. The coated optical fiber 1201 includes an optical fiber 1202 at the center thereof and a first coating layer 1203 and a second coating layer 1204 made of an ultraviolet ray curing type resin are sequentially applied on a periphery of thereof and, further, a color layer 1205 is formed on a periphery the second coating layer 1204 by applying color ink made of an ultraviolet ray curable resin. A plurality, (usually 4n (n being 2, 3, . . . ) pieces, and 8 pieces in this embodiment) of optical fibers 1202 are arranged in a row in parallel. The overall coating layer 1206 is filled in gaps defined between respective coated optical fibers 1201 which are arranged in parallel so as to integrate the coated optical fibers 1201 and is made of, for example, an ultraviolet ray curable resin which is applied to outer peripheries of the coated optical fibers 1201 with a thickness of h=10 μm or less. FIG. 40A is a plan view of the above-mentioned optical fiber ribbon. As clearly shown in FIG. 40A, the overall coating layer 1206 is intermittently peeled off in the longitudinal direction so that intermittent portions 1207 having no coating layers and exposing the coated optical fibers 1201 are formed. That is, coating portions 1208 where the coating layer 1206 is left and the above-mentioned intermittent layers are alternately arranged. FIG. 40B shows a transverse cross section of the portion which constitutes the above-mentioned coating portion 1208.
Further, in Japanese Unexamined Patent Publication Sho. 63(1985)-13008, as shown in FIG. 41, in an optical fiber ribbon 2100, a coated optical fiber 2101 is constituted of a glass fiber 2101a which constitutes a core and a primary coating layer (buffer layer) 2101b which is formed on an outer periphery of the glass fiber 2101a. A plurality of coated optical fibers 2101 are arranged in parallel like a ribbon and resin adhesive portions 2102 are formed at a fixed interval in the lengthwise direction of the ribbon. The resin adhesive portions 2102 are formed of an ultraviolet ray curable resin such as an epoxy acrylate resin, an polybuthadiene acrylate resin, a silicone acrylate resin, for example.
Further, In U.S. Pat. No. 4,147,407, as shown in FIG. 42, an optical fiber ribbon 2110 is formed such that a two-layered coating consisting of a primary coating 2112 and a secondary coating 2113 is applied to an outside of each glass fiber 2111 thus forming an optical fiber 2114. A plurality of these optical fibers 2114 are bundled and the secondary coatings 2113 which are once cured are melt by a solvent thus forming a common coating by melting each other.
Further, in Japanese Accepted Patent Publication Sho. 63(1988)-2085, as shown in FIG. 43, an optical fiber ribbon 2120 constitutes an optical fiber 2123 by forming a coating 2122 on an outside of a glass fiber 2121 and a roving is vertically attached to both sides of the optical fiber 2123 as reinforcing glass fibers 2124. Then, a ribbon-like interwoven body 2126 is obtained by weaving these reinforcing glass fibers 2124 as warps and glass fibers 2125 as wefts, and the interwoven body 2126 is impregnated with a thermosetting resin 2127 and is set to a half-cured state. In this case, the reinforcing glass fibers 2124 which are attached to both sides of the optical fiber 2123 are fastened by the glass fibers 2125 which constitute the wefts and wraps the optical fibers 2123.
Recently, along with the increase of demand for optical communication systems, optical fiber cables using the above-mentioned optical fiber ribbons which constitute optical transmission paths are popularly installed using conduits, poles or the like.
Generally, as the optical fiber cable installed in a communication trunk route such as the conduits and the poles, a tape slot type optical fiber cable has been popularly used (for example, see General Catalogue of optical fiber cable network wiring system, Sumitomo Denki Kogyo, Co., Ltd. issued on August, 2002, page 9).
FIG. 44 shows an example of a related-art tape slot type optical fiber cable.
As shown in FIG. 44, in the related-art tape slot type optical fiber cable 3050, a plurality of optical fiber ribbons 3060 are housed in grooves 3053 formed in a spacer 3052 having a tensile strength body 3051 at the center thereof. The optical fiber cable 3050 is a 100-core type optical fiber cable, wherein five sheets of four-fibered optical fiber ribbons 3060 are stacked and housed in each one of five grooves 3053. Further, respective grooves 3053 are formed spirally in one direction in a state that they are arranged parallel to each other along the longitudinal direction. Alternatively, there also exists a n optical fiber cable in which the respective grooves 3053 are formed spirally in the alternatingly inverted manner in the circumferential direction while maintaining a state in which they are arranged parallel to each other in the longitudinal direction. In general, the spacers in which the grooves are formed spirally in one direction are referred to as one-direction twisted spacers and the spacers in which the grooves are formed spirally in the alternatingly inverted manner are referred to as SZ spacers.
Further, to prevent the removal of the optical fiber ribbons 3060 from the grooves 3053, a press winding 3054 is wound around a periphery of the spacer 3052 and, at the same time, an outside of the press winding 3054 is covered with a plastic sheath 3055.
The tensile strength body 3051 is a tensile strength body which is provided for preventing the direct transfer of a tensile strength to the optical fiber ribbons 3060 when the tensile strength is applied to the optical fiber cable 3050 and a steel wire is used as the tensile strength body, for example.
The optical fiber ribbons 3060 are arranged such that four optical fibers having an outer diameter of 250 μm are arranged in parallel such that they are brought into contact with each other, and the whole optical fibers are covered with an ultraviolet ray curable resin and are formed into a ribbon shape. With respect to the contour of the optical fiber ribbon 3060, for example, a thickness thereof is approximately 0.3 mm to 0.4 mm and a width thereof is approximately 1.1 mm. Five optical fiber ribbons 3060 which are housed in the inside of one groove 3053 are stacked in a state that they are brought into close contact with each other.
Further, as another configuration of the optical fiber cable installed in a communication trunk route such as conduits, poles or the like, optical fiber ribbons are housed in a tube-like elongated body. For example, as a loose tube type fiber cable, a following fiber cable has been disclosed (see Proceedings of the 51st IWCS (International Wire & Cable Symposium) pages 22 to 25).
As shown in FIG. 45, six sheets of 12-fibered optical fiber ribbons 4102 each of which collectively covers 12-fibered optical fibers 4101 are interwoven and are housed in the inside of a tube 4103, and four pieces of these tubes 4103 are twisted together around a center tensile strength body 4104 in an alternatingly inverted manner in the longitudinal direction and, a sheath 4105 is applied thereto.
Although the detailed structure of the 12-fibered optical fiber ribbons 4102 is not described in detail, usually, coated optical fibers having an outer diameter of 250 μm are arranged in parallel and the whole coated optical fibers are covered with an ultraviolet ray curable resin thus forming the optical fiber ribbon in a ribbon shape. With respect to outer sizes of the ribbon-shaped body, for example, a thickness thereof is approximately 0.3 mm to 0.4 mm and a width thereof is approximately 3.1 mm.
As an optical fiber cable served for an application such as FTTH (Fiber To The Home) or the like, a drop cable which is distributed and dropped from an overhead wiring cable for every one or a plurality of optical fibers can be named (for example, General Catalogue on Optical fiber cable network wiring system, Sumitomo Denki Kogyo Co., Ltd. issued on August, 2002, page 13). An example of an optical fiber cable used as the drop cable is shown in FIG. 46.
As shown in FIG. 46, a related-art optical fiber cable 5100 is configured such that an element portion 5107 and a messenger wire portion 5108 are connected by a neck portion 5105.
In the element portion 5107, an optical fiber 5101 and two tensile strength bodies 5102 are covered with a sheath 5103 made of a thermoplastic resin. The optical fiber 5101 is formed by covering an outer periphery of a glass fiber with an ultraviolet ray curable resin, wherein an outer diameter thereof is 250 μm, for example. As the tensile strength body 5102, a linear body made of steel or fiber reinforced plastic (FRP) is used, wherein a contour of a cross section of the tensile strength body 5102 is formed in a circular shape. By collectively covering the optical fiber 5101 and the tensile strength bodies 5102 with the sheath 5103, an external force such as a tensile force or the like added to the optical fiber cable 5100 is received by the tensile strength bodies 5102 so as to protect the optical fiber 5101 from the external force.
Further, two notches 5104 are formed in an outer periphery of the element portion 5107 such that the notches 5104 are directed to the optical fiber 5101. The notches 5104 are provided for easing the taking out of the optical fiber 5101, wherein at the time of taking out the optical fiber 5101, cuts are formed in portions of the sheath 5103 between two notches 5104 and these portions are torn.
The messenger wire portion 5108 is configured to have strength to support the optical fiber cable 5100 overhead and is formed by covering a support line 5106 made of steel, FRP or the like with a sheath 5103.
Further, the neck portion 5105 is integrally formed with the element portion 5107 and the messenger wire portion 5108 using the same resin as the resin of the sheath 5103 for the element portion 5107 and the messenger wire portion 5108.
Although the optical fiber cable 5100 having one optical fiber 5104 is illustrated here, among the related-art drop cables, there exists a drop cable in which two optical fibers are arranged in parallel or, as shown in FIG. 47, there exist a drop cable which includes an optical fiber ribbon 5101a which is produced by a forming a plurality of optical fibers into a ribbon.
The related-art optical fiber ribbon 5101a is formed by arranging four optical fibers having an outer diameter of 250 μm in parallel in a state that four optical fibers are brought into contact with each other and the whole optical fibers are covered with an ultraviolet ray curable resin in a ribbon shape. The size of the outer contour of the optical fiber ribbon is such that a thickness thereof is approximately 0.3 mm to 0.4 mm and a width thereof is approximately 1.1 mm.
Here, with respect to the above-mentioned optical fiber cable which is installed in the communication trunk route shown in FIG. 44 and FIG. 45, to wire the optical fiber to a subscriber-side building or the like from a housing station, there may be cases in which the housed optical fiber ribbons are pulled out and any arbitrary optical fibers out of the pulled out optical fiber ribbons are connected with optical fibers at the subscribers side.
In the related-art tape slot type optical fiber cable shown in FIG. 44, first of all, the sheath and the press winding are peeled off from an arbitrary portion of the installed optical fiber cable by a given length and, thereafter, desired optical fiber ribbons are pulled out from the grooves. Then, given optical fibers are branched from the pulled-out optical fiber ribbons and are connected to the optical fibers at the subscriber side.
Further, with respect to the related-art loose tube type optical fiber cable shown in FIG. 45, first of all, the sheath is peeled off from an arbitrary portion of the installed optical fiber cable by a given length, the desired tubes are pulled out and, thereafter, the coatings of the tubes are removed so as to pull out the desired optical fiber ribbons. Then, given optical fibers are branched from the pulled-out optical fiber ribbons and are connected to the optical fibers at the subscriber side.
Further, with respect to the optical fiber cable 5100 shown in FIG. 46, when the optical fiber cable 5100 is introduced into the inside of a housing from overhead, the messenger wire portion 5108 for supporting the optical fiber cable overhead becomes unnecessary and hence, the neck portion 5105 is torn so as to divide the element portion 5107 and the messenger wire portion 5108. Then, the optical fiber cable which is constituted of only the element portion 5107 is wired in the housing.
With respect to the optical fiber cable 5100a shown in FIG. 47, after wiring the optical fiber cable 5100 in the inside of a housing, the coated optical fiber ribbon 5101a is taken out and the arbitrary optical fibers out of the taken-out optical fiber ribbon 5101a are connected to optical fibers at the subscribers side.
In this case, first of all, the sheath 5103 is torn at an arbitrary portion of the wired optical fiber cable 5100a so as to take out the optical fiber ribbon 5101a. Then, desired optical fibers are branched from the taken-out optical fiber ribbon 5101a and are connected to the optical fibers at the subscribers side.
Since the optical fiber cable which is already wired includes optical fibers through which optical signals are transmitted, there has been requested an operation to branch optical fibers which are not used as transmission paths from an intermediate portion of the optical fiber ribbon in which some optical fibers are used as the transmission paths while suppressing the deterioration of transmission quality (so-called live-line branching operation). Accordingly, in branching the desired optical fibers, a demand for a branching method which is referred to as an intermediate post branching in which desired optical fibers are branched from an intermediate portion of a taken-out optical fiber ribbon without cutting the optical fiber ribbon has been increasing.
However, with respect to the optical fiber ribbon which is housed in the related-art optical fiber cable, it is difficult to remove resin which covers a plurality of optical fibers and, particularly, under the current situation, it is difficult to perform the intermediate post branching by selecting one optical fiber out of the plurality of optical fibers.
For example, in an attempt to shave off the resin using a sandpaper or a tool such as a planer, there exists a possibility that the optical fiber is damaged or cut.
Under such circumstances, in the related art, the intermediate post branching cannot be performed and hence, to branch a desired optical fiber, all of a plurality of optical fibers which are integrally formed as an optical fiber ribbon are cut and, thereafter, a single optical fiber is branched from the cut portion of the optical fiber ribbon. Accordingly, it is impossible to perform the live-line branching operation of the optical fiber ribbon including the optical fibers in the using state (that is, in the live state) as the transmission path.
Further, when the optical fiber ribbon is cut, the remaining optical fibers other than the optical fibers which are connected at the cut portion cannot be used as the transmission path thus pushing up a cost for constructing an optical communication network.
Further, recently, the demand for long-distance transmission of the high-speed signals of high packing density has been increasing in the information communication and the reduction of polarization mode dispersion (PMD) of the optical fiber which becomes a factor to restrict the long-distance transmission has been requested. However, in the optical fiber cable shown in FIG. 45 which houses the optical fiber ribbon in the tube, the ribbon is twisted in the tube and, further, the tube is twisted around the tensile strength body at the center and hence, the ribbon is deformed in the tube and hence, there arises a drawback that the refractive birefringence is generated due to a stress which the optical fiber receives from resin so that the PMD is increased.